We propose a comparative analysis of fertility patterns based on World Fertility Survey data from about forty less developed countries. The main goal of this analysis is to better our understanding of how social, economic, and ethnic/cultural fertility differntials are established. We will employ a multi-level approach that exploits the full potential of the World Fertility Survey data for comparative analysis. Multi-level analysis will separate micro and macro mechanisms responsible for varying fertility patterns across social groups, within and between societies. Since the quality of comparative analysis greatly depends upon a detailed micro specification, part of our study will pay close attention to the mechanisms responsible for differences in the fertility behavior of individual women. First, we will separate the fertility process into components: onset of fertility, the pace of family-building, and cessation behavior--all of which together produce completed family size. Second, we will trace the fertility effects of education, previous and current work experience, husband's occupation, rural-urban residence, religion and/or ethnicity through their effects on intermediate variables, including age at marriage, marital duration and stability, infant and fetal mortality, breastfeeding patterns, and contraceptive practice. In the comparative part of the analysis, we will investigate cross-societal variation in the relationships that account for intra-societal fertility differences. Macro data collected from secondary, international sources will be used to explain variability in the micro-level effects. At both the micro and macro levels, the analysis will be sensitive to the problems engendered by the use of one-time sample surveys to obtain information on cohorts at different stages in the reproductive years.